Two-way repeater



Aug. 4, 1925.

J. 5. JAMMER TWO-WAY REPEATER Filed June 1923- I W e/War. v Jamfifi Jam/m r fiy /4/7j' Patented Aug. 4, 1925.

UNITED STATES v 11,548,039 P-ATENTQFFICE.

JACOB s. JAMMER, or NEW YORK, N. Y.', ASSIGNQR T0 wns'rnmv ELECTRIC COMPANY,

rncoaroaa'rnn, or NEW 01 K, n. Y., A CORPORATION or'nnwaronx.

TWO-WAY REPEA'IER.

Application. filed June 29, 1923. Serial No. 648,433.

To all whom it may 00mm,-

1 ing is a full, clear, concise, and exact description.

This invention relates to a two-way amplifying repeater such as is employed in multiplex carrier current telephone and teleraph systems wherein the different channelv requencies for transmission in one direction are grouped in a different frequency ran e from that employed for transmission in t e opposite direction.

Such two-way vrepeaters, inbperatiQn,

have. theiriamphfiers connected in opposite- 1y directed repeating channels forming a v loop and the total gain of the amplifiers -mu.st not exceed" thetotal loss withinthe loop, since otherwise the repeater will sin or generate oscillations; There shoul therefore, be a substantial singing margin which may be defined adequately as the difference between the total gain in the loop and that gain which fora given condition will just cause the repeater to sing. Unless a substantial-singing margin is provided the transmission characteristic of the repeater will be VGIY'IIlIlCll distorted due to currents circulating around the loop.

Among the objects of the invention are:

To increase the singing margin of a twoway repeater without materially increasing the cost thereof.

To provide. a two-way repeater. wherein the singing margin is substantially increased without materially increasing the over-all transmission loss.

To provide an eflicient two-way repeater which may be economically manufacturedand maintained.

Two-way repeaters .of the prior art have been coupled to the transmission line sec-.

tions by means of either (1) hybrid coils and associated line balancing networks which render the two-way repeating channels conjugate, or (2) directional filters which separate the oppositely directedtransmissions.

The use of hybrid coils and balancing net works has the disadvantage that such networks are very expensive to manufacture and maintain and it is difiicult, ifnot wholly impossible, to maintain the line balance under the changing conditions of weather,

temperature, etc; Furthermore, the. prescure of each hybrid coil and associated balancing network introduces an over-all loss of several standard cable "miles. I

The directional filters are-free from some of these objections in that it is not necessary to balance the lines when they are'employed and the loss of over-all transmission is reduced. Such filters, however, arevery expensive to manufacture and their cost increases very rapidly as the energy level of objects thereof are realized by providing in each of the oppositely directed repeating channels input and output directional filters 1 and coupling the channels to the respective line sections by unbalanced hybrid coils or by hybrid coils whose associated line balancing networks are replaced by paths which have substantially no resistance or impedahce.

By such an arrangement, very materially cheaper directional filters may be employed for a particular energy level to be transmitted and for the attenuation to be introduced thereby. The loop loss and consequently .the singing margin is therefore materially increased without substantially increasing the over-all transmission loss.

The invention is illustrated as applied to a two-way amplifying repeater for use .in a multiplex carrier current telephone or telegraph system but it is to be understood that it may also be applied to two-way amplifying repeaters for use in. other signaling systems wherein the frequencies of the waves transmitted in one direction are in a different frequency range from that embracing the waves transmitted in the opposite direction.

The illustrated two-way repeatertwhich comprises two one-way repeating channels RW and'RE is adapted to couple two transmission line sections and'E,

The currents incoming to the repeater station from the line section W are amplified in the repeating channel RVV and the currents so amplified are delivered to line section' ,E. Likewise the currents incoming from line section E are amplified in the repeater channel RE and the currents so amplified are delivered to the line section \V.

The ciirrents incoming from the line section WV are of higher frequencies than those incoming from line section E and as will more fully appear hereinafter, the respective repeating channels are quency discriminating lters which direct the-incoming currents to the proper channels.

The repeating channel RVV includes an input directional filter WIF and an amplifying structure WA and an output directional filter WOF.

The two directional filters are designed to pass currents of the frequencies to be repeated by the amplifying structure WA and to suppress currents of all other frequencies. These filters may be of the type disclosed in United States patents to Campbell No.71,227,113 and 1,227,114 dated May 22, 191 i The amplifying structure WA may be of any well known type, such, for example, as that disclosed in the U. S. patent to Raibourn No. 1,413,357 dated April 18, 1922.

The repeating channel RE includes input directional filter EIF, anamplifying structure EA and an output directional filter EQF.

The input and output directional filters EIF and EOF are similar to the directional filters employed in the repeating channel RVV, except that they are designed to pass currents of the particular frequencies to be amplified by the amplifying structure EA and to suppress currents of all other frequencies.

The amplifying structure EA may be of any well known type, such, for example as that disclosed in the Raibourn patent, supra.

The line section W is coupled to the two repeating channels by means of a .threewinding transformer WT, the terminals of two of the windings being conductively connected to the line wires. The free terminals of these two line windings are joined by an element 2 which is substantially free from both resistance and impedance. The third winding of the transformer WT is connected to the input of the directional filter WIF. The output of the directional filter EOF is connected through a transformer T to the midpoints of the line windings of transformer WT, thereby bridging the output of the repeating channel RE across the midpoints of the line windings of this transformer.

The output impedance of directional filter ing channels.

rovided With fre- EOF is high to currents incoming over the line section 1V, and the input impedance of directional filter \VIF is high tocurrents transmitted from the repeating channel RE to the line section 1V.

A similar transformer ET is employed to connect the line section E to the two repeat The free terminals of the line windings of transformer ET are joined by a connection 3 which may be exactly like connection 2. The third winding of transformer ET is connected to the input directional filter EIF. The output of directional filter \VOF is connected from the transformer T to the midpoints of the line windings of transformer ET.

The output impedance of directional filin the repeating channels thereof are coupled to the line sections by three-winding transformers provided with networks for balancing the respective line sections so as to render the repeating channels conjugate, are difiicult to maintain because it is practically impossible to maintain the line sections balanced under all changing operating conditions. This is true whether or not directional filters are employed. The use of the three-winding transformers and associated line balancing networks introduces a loss of several standard cable miles to the currents to be repeated from one line section to the other, and the loop loss introduced thereby, if there is a perfect balance, is infinite.

\Vhen directional filters without three winding transformers and associated balancing networks are employed, substantially all of the attenuation in the loop to currents of frequencies outside of the transmitting range of the filters must be introduced by the filters. As the magnitude of the currents to be attenuated increases, the cost of the filters increases very rapidly.

Even when both filters and three-winding transformers with associated balancing networks are employed as in the Raibourn patent, supra, an overall transmission loss of several standard cable miles for each transformer and network is introduced.

It has been demonstrated experimentally and proven mathematically that the use of three-winding transformers, the free terminals of whose line windings are connected by elements of substantially no resistance put and output directional filters of the coupled repeating channels. i 1

Such a combination wherein :is-employed and adaptations.

The invention claimed is: p 1 The combinationof a two-way repeater having two asymmetric repeatingchannels for repeating signals in opposite directions,

each channelincluding an amplifier and an input directional filter and an output directional filter, two transmission line sections,

a three-winding transformer associated with each line section and having terminals of two of its windings conductively connected to the associated line wires, and its third winding conductively connected to one of the channels, the other channel being 'tions whereby singing in the repeater sys tem is likely to occur, and attenuating the' bridged across the ,midpoints of the line avindings of the transformer, and an element for eacht'ransformer connected across the other terminals of its line windings, each of said elements having an impedance low in comparison to that of the associated line section. v a

2. The combination of a two-way repeater having 'two asymmetric repeating channels for repeating signals in opposite directions, each channel including an amplifier and an input directional filter and an output directional filter, two transmission line sections,

' a three-winding transformer associated with each line section and coupling the channels thereto, the transformer, having a terminal of each of two of its windings conductively connected to the associated line section and the other terminals of said two windi'ngs'be:

ing coupled by a connection of substantially no resistance or impedance.

therefore, less ex- A 3. The combination of a-two way'repeater for repeating signals in opposite directions,

each channel including amplifying means v and frequency discriminating means each side of the amplifying means, two transmission line sections, and a three-winding transformer for each line section having twobfv its windings connected. in series therewith and its third winding connected to one of havingtwo asymmetric repeating channels the frequency discriminating means of one channel, .suchfrequency discriminating means having a high impedance to currents transmitted from theother channel to' the line section, one of the discriminating means of the other channel being connected to. the midpoints of'the transformerline-windings and having a high impedance to currents incoming from the line section. A.

4. In a two-way repeating system for repeating over two asymmetric amplifying channels oppositely directly transmissions incoming over line sections coupled to the repeating system, the method of repeating which comprises unbalancingthe line sec-' circulating currents so set up whereby sing ingis prevented;

5. -A two-way repeater for a wave transmission system having two line sections,

wherein the waves transmitted in opposite directions through the system are within mutually exclusive frequency ranges, com prising two oppositely directed'one-way' repeating paths, each containing an amplifier and frequency selective means selective of the wave frequencies transmitted in the corresponding direction only, said repeating 

